Stromatactis: A sedimentary structure characterized by a horizontal or nearly flat bottom, up to about 10 centimeters in diameter, and an irregular or convex-upward upper surface, consisting of sparry-calcite cement, usually in the central part of a reef core. They have been interpreted as infillings of original cavities caused by the burial and decay of soft-bodied but rigid frame-building organisms, although they may represent syngenetic voids in calcareous sediments. (Definition from Jackson, J.A., ed., 1997, Glossary of geology [4th ed.]: Alexandria, Va., American Geological Institute, 769 p.)